Colors in rustc's error mesages are lost

[alexcrichton]

🐛 Bug description

When compiling code with wasm-pack build the compiler's error messages are not printed with colors.

🤔 Expected Behavior

The compiler's colors come through!

👟 Steps to reproduce

If you create a blank src/lib.rs with only one token in it, x (invalid rust code), then wasm-pack build will show the compiler's error but without colors

[ashleygwilliams]

this was solved by the PR that moved us toward our new output strategy :) closing.